The argument for vegetarianism on ethical grounds is a logical fallacy, because it pretends that there are no instances where one could consume an animal without killing it (or having it killed). This is clearly false: one could consume an animal which has died of natural causes, for example. Note that some vegetarians employ similar scenarios to justify their use of animal products (e.g., leather shoes), and rightly so.
Instead of arguing for vegetarianism on ethical grounds, vegetarians should instead be arguing against the killing of animals on ethical grounds. This may provide them with less opportunity to evangelize their dietary choices, although it need not, if they can work vegetarianism into the conversation in a non-fallacious manner (i.e., if they simply present vegetarianism as one option in a grab-bag of assorted lifestyle choices which might reduce human impact on other species).
In short: vegetarianism precludes the eating of meat; an ethical stance against the killing of animals does not.
Posted by DD 